The pilot who appears to have deliberately crashed a plane carrying 149 others into the French Alps received psychiatric treatment for a "serious depressive episode" six years ago, German tabloid Bild reported on Friday.

Prosecutors in France, after listening to the cockpit voice recorders, offered no motive for why Andreas Lubitz, 27, would take the controls of the Airbus A320, lock the captain out of the cockpit and deliberately set it veering down from cruising altitude at 3,000 feet per minute.

Citing internal documents and Lufthansa sources, Bild said Lubitz spent a total of one and a half years in psychiatric treatment and that the relevant documents would be passed to French investigators once they had been examined by German authorities.

Lufthansa Chief Executive Carsten Spohr told a news conference on Thursday that Lubitz had taken a break during his training six years ago, but did not explain why and said he had passed all tests to be fit to fly.

"Six years ago there was a lengthy interruption in his training. After he was cleared again, he resumed training. He passed all the subsequent tests and checks with flying colors. His flying abilities were flawless," Spohr said.

A Lufthansa spokeswoman said on Friday the airline would not comment on the state of health of the pilot.